Our research investigates the roles of language in the production and subsequent use of legal documents, or charters, in the early Middle Ages (c.700–c.1100). In particular, the project examines the relationship between Latin and the vernacular in these records. Charters from Anglo-Saxon England offer remarkable evidence for exploring this topic, as they contain Old English alongside the Latin. In comparison, charters from eastern Francia (an area roughly spanning the Rhineland, Switzerland and Bavaria) – which was non-Romance-speaking, like Anglo-Saxon England – were almost always written in Latin, never developing the bilingualism which characterises the Anglo-Saxon material. These linguistic features have largely been taken for granted. Taking our cue from recent work on sociolinguistics, historical linguistics, the interaction between oral and literary cultures, and the uses of the written word, we shall assess comparatively the appearance of vernacular language in Anglo-Saxon and Frankish charters in order to better understand the social, cultural and linguistic history of the early Middle Ages.